The U.S. Pat. No. 3,588,382 describes a pressure gradient microphone of the electret type with the electret being divided into semicircular sections, said sections being positively or negatively charged. It is difficult to manufacture good pressure gradient microphones according to this principle for measuring purposes. Such microphones are, apart from being sensitive to pressure gradients, also sensitive to pressure, i.e. to pressure equally distributed all over the membrane. The polarized sections divide the microphone into separate transducer sections, each section contributing to the signal of the microphone. Ideally, the contributions of the sections should neutralize each other with equal pressure all over the membrane whereby the microphone should transmit no signal. Due to different charges, unequal distances between the membrane and the charged sections, unequally distributed membrane voltages etc. between the components this can never be achieved in practice. That is why such pressure gradient microphones are not used for the acoustic measuring of particle speed and sound intensity, although it would be an advantage compared to the state of the art.